Zirconium alloys



United States Patent.

P y No Drawing. Filed Dec. 11, 1963, Ser. No. 329,856 Claims priority, application Great Britain, Dec. 19, 1962, 47,937/ 62 5 Claims. (Cl. 75-177) This invention relates to alloys of zirconium possessing a high resistance to corrosion in steam at a temperature within the range of approximately 280 C. to 500 C. and also in carbon dioxide, in air and in carbon dioxide/air mixtures.

Zirconium base alloys containing 0.5% to 1.5%, by weight, copper and from 0.25% to 1.5%, by weight, tung sten, exhibit a considerable resistance to corrosion by carbon dioxide at elevated temperatures. These alloys also exhibit good creep properties at temperatures of about 550 C. Both creep resistance and resistance to corrosion may be greatly improved by heat treatment of the alloys, for example by heating at a temperature of about 950 C. followed by tempering at a temperature within the range 650 C. to 700 C. Such heat treatment results in an alloy with very high resistance to creep and with resistance to corrosion better than on annealed material, i.e., material heat treated by annealing at a temperature below 800 C.

For use in steam atmospheres at temperatures within the range 280 C. to 500 C., however, an alloy must have a high solubility for hydrogen. This is important for two reasons:

(a) If the alloy has a low solubility for hydrogen, rapid embrittlement caused by the precipitation of needles of zirconium hydride can occur during exposure of the alloy to high temperature steam, and

(b) Zirconium hydride needles precipitated at the specimen surface disrupt the protective oxide film, which normally develops on the surface, and expose the fresh underlying region of the alloy to the steam. This eifect, known as oxide spalling, leads to rapid corrosion of the alloy,

Disruption of the oxide film on the above mentioned zirconium-copper-tungsten alloys and by the above mentioned effects has been observed in high pressure steam at temperatures in the region of 500 C. It has now been found that this oxide spalling can be prevented by the addition of niobium to the ternary alloy.

A zirconium alloy in accordance with the present invention consists, essentially, by weight of 0.5 to 1.5% copper, 0.25 to 1.5% tungsten and 0.2 to 3.0% niobium.

By essentially is meant an alloy containing as well as the constituents specified any impurities inherently present in any of the alloy constituents and unspecified ingredients deliberately added to the alloy in order to change its composition but not materially aifecting the basic and novel properties.

These alloys find particular use as the constituent material for the pressure tubes of steam generating, heavy water moderated, nuclear reactors.

Conditions arise in steam generating, heavy water moderated nuclear reactors such that a member fabricated from a zirconium alloy is exposed on one side to steam at temperatures within the range 280 C. to 500 C. and to air, and a mixture of air and CO at different regions on the other side. Thus, any alloy used in this way must See have adequate resistance to corrosionin all three atmospheres. While resistance to corrosion of zirconium-copper-tungsten alloys in steam is increased by the addition of niobium, the resistance of the alloy to corrosion by air and by C0 is reduced. By suitable choice of composition of the quaternary alloys, according to the invention, their corrosion resistance in steam, in air, and in air/CO can be made adequate.

The following four examples are given of preferred quaternary alloys falling Within the range above specified as constituting the invention:

Example a0.5% Cu, 0.5% W, 1.0% Nb, remainder zirconium.

Example b1.0% Cu, 1.5% W, 0.5 Nb, remainder zirconium.

Example c1.0% Cu, 0.5% W, 1.0% Nb, remainder zirconium.

Example d-1.5% Cu, 1.0% W, 0.5% Nb, remainder zirconium.

Corrosion tests carried out on alloys within the ranges of composition claimed and on known commercially available alloys used in steam and C0 atmospheres respectively gave the following results. The alloys are listed in order of corrosion resistance under each condition.

Wet steam at 280 C. and 800 p.s.i.g.Weight Alloy gain, mg./cm.

1,000 hours 2,000 hours Zircoloy-4 0. 124 0. 126 Zr, 2.5% Nb 0. 24 0.310 Zr, 05% Cu, 0.5% W 0.169 0.352 Zr, 0.5% 011, 0.5% W, 0.5% Nb 0. 210 0. 421 Z1, 1.0% Cu, 0.5% W, 1.0% Nb (Example 0). 0. 237 0. 428 Zr, 1.5% Cu, 0.5% W, 2.0% Nb 0.277 0. 466 Zr, 0.5% Cu, 0.5% b 0. 5 0.6 Zr, 1.5% Cu, 1.0% W, 0.5% Nb (Example (1) 0. 339 0.622 Zr, 0.5% Cu, 0.5% W, 1.0% Nb (Example a) 0. 469 0. 755

Dry steam at 500 C. and 800 p.s.i.g./Weight gain,

mg. em.

1,000 hours 2,000 hours Zr, 0.5% Cu, 0.5% W, 1.0% Nb (Example a) 1. 50 2.11 Zr, 0.5% Cu, 0.5% W, 0.5% Nb 1.38 2. 40 Zr, 1.0% 011, 0.5% W, 1.0% Nb (Example c) 1. 46 2. 55 Zr, 0.5% Cu, 0.5% W, 2.0% Nb 1.76 2.67 Zr, 1.5% Cu, 1.0% W, 0.5% Nb (Example (1). 1. 30 2. 79 Zr, 2.5% Nb 3. 21 5. 5 Zireoloy-4 Complete disintegration, Zr, 0.5% Cu, 0.5% W 25 hours Moist 002 at 700 C. and 0 p.s.i.g.-Weight gain, mgJcm.

200 hours 1,000 hours Zr, 1 .5% Cu, 1.0% W, 0.5% Nb (Example (1). 5. 14.61 Zr, 0.5% Cu, 0.5% Mo 5. 00 17. 00 Zr, 1.0% Cu, 0 5% W, 1.0% Nb (Example 0). 6. 44 19. 74 Zr, 0.5% Cu, 54 Zr, 0.5% Cu, Zr, 0.5% Cu, Zr, 0.5% Cu, Zr, 2.5% Nb Zucoloy-4 What we claim is: 1. A zirconium alloy consisting essentially by weight of 0.5% to 1.5% copper, 0.25% to 1.5% tungsten, 0.2% to 3.0% niobium, and the remainder zirconium.

2. A zirconium alloy consisting essentially by weight of References Cited by the Examiner tungsten, 1.0% niobium and the re- UNITED STATES PATENTS 3. A zirconium alloy consisting essentially by weight of 2,924,518 2/1960 Rama 75 177 1.5 %d copper, 1.0% tungsten, 0.5% niobium and the re- 5 FOREIGN PATENTS main er zirocnium.

4. A zirconium alloy consisting essentially by weight of 630239 10/1961 Canada 0 5% copper 0 5% tungsten 1 0% niobium and the re- 1281198 11/1961 France 884,682 12/1961 Great Britain.

mainder zirconium.

5. A zirconium alloy consisting essentially by weight of 10 DAVID RECK Primary Exammer- 1.0% copper, 1.5% tungsten, 0.5 niobium and the re- W, C, TOWNSEND, C, N, LOVELL, mainder zirconium. Assistant Examiners. 

1. A ZIRCONIUM ALLOY CONSISTING ESSENTIALLY BY WEIGHT OF 0.5% TO 1.5% COPPER. 0.25% TO 1.5% TUNGSTEN, 0.2% TO 3.0% NIOBIUM, AND THE REMAINDER ZIRCONIUM. 